A 30-nΩ Accuracy Low Power Two-Step Ratiometric Shunt Resistance Measurement System Using a Switching Regulator- Based Current Generator for Shunt- Based Current Sensors

This article presents a high-precision resistance measurement system for shunt-based current sensors in battery-powered vehicles to calibrate the resistance drift of the shunt resistor ( ${R}_{\text {S}}$ ) caused by aging. To measure the resistance of a $25~\mu \Omega ~{R}_{\text {S}}$ using a $10\Omega $ reference resistor ( ${R}_{\text {REF1}}$ ) with a ratio of 400000:1, we proposed a two-step ratiometric resistance measurement technique using a reference resistor with an intermediate resistance value of 10 m $\Omega $ . The ratiometric measurement cancels the drift and noise of a test current by synchronously measuring the voltages across the resistors using analog front-end (AFE) circuits. A high-side ratiometric measurement circuit uses a dc test current. A low-side ratiometric measurement circuit uses an ac test current ( ${I}_{\text {E2}}$ ) at 162.8 Hz generated by a two-stage switching regulator-based current generator (SRCG) and a lock-in technique to reduce the influence of the thermal electromotive force (EMF) of the ${R}_{\text {S}}$ . The two-stage SRCG consisting of a charge sampling stage and a switching regulator stage reduces both power consumption and inrush current from the power supply. It operates with a 15.6 kHz switching signal modulated at 162.8 Hz to reduce the size of LC components. The SRCG and AFEs operate synchronously, and all spurious noise is filtered by a third-order CIC filter in a digital domain. The implemented system demonstrates less than 0.12% (30 n $\Omega $ ) resistance measurement error with a $25~\mu \Omega ~{R}_{\text {S}}$ , and the SRCG generating the ac test current of 1 Arms draws 43 mA from the power supply.

I. Introduction

Shunt-Based current sensors are widely used in battery management systems of battery-powered vehicles with current ranges up to a few kA due to their low current offset and low gain error, which enables accurate estimation of state-of-charge (SOC) of the batteries [see Fig. 1(a)] [1], [2], [3]. The SOC is defined as the percentage of the available charge to the current full-capacity charge stored in the battery [4]. The SOC is monitored using the Coulomb counting method, which is estimated from the integral value of the battery current [5]. Fig. 1.

(a) Battery management system for a battery-powered vehicle. (b) Resistance measurement system in shunt-based current sensor [23], [24].